[esbranson]

The rules of engagement are probably to consider everyone hostile unless and until proven otherwise. If you're a California male citizen for example, you probably have no clue that you've been declared a combatant. By law. (Military and Veterans Code § 122.) North Koreans are probably less sexist and ageist, and less ignorant and naive than Californians to boot. On a state-owned vessel.

Enemy combatants don't magically get immunity from war when they don't have a weapon on them, nor do military forces have to go into a state property and politely ask everyone without a weapon if they're an enemy combatant before they can fire on it and turn everyone into dust. Nor are they required to refrain from engaging enemy forces because someone else is likely to get hurt. Your entire line of assumptions and the questions that flow from them is detached from reality.

The military law of your jurisdiction, at a minimum, would be a good book to read, if you can afford it. I think a one-time purchase from Thomson Reuters for the California Code would cost you $41,000 USD and a pretty onerous contract. If you tried to take one from a library, I'm sure they'd only give you a couple nights in jail and a year of probation. I think you can get Hong Kong's for $90,000 if that's where you live.